Comments

It sounds like your sensor just puts out simple high/low pulses per revolution. If so, you could probably use one of the counters in a cog to detect the pulse transistions. What voltages are we talking about here 12v, 5v or 3.3v? You will probably need to use a resistor or a transistor or level shifter to condition the incoming signal to be appropriate for the input pin of the propeller board being used.